An arrangement of an ultrasonic transducer with a filter element is known from European Patent, EP 1 340 964 B1. Such arrangement includes a signal radiating bending plate, which feeds body sound from its edge into the filter element. In this way, the ultrasonic signal is, indeed, centered in the middle; however, the radiating area is very small. The effective total structure of the arrangement in this publication has additionally a frequency spectrum, in which rotation- and axial modes lie very near to one another and below a frequency range of 80000 Hz, the usual frequency range of the wanted signal. This means that the choice of the frequency for the wanted signal is extremely limited or one must compensate measurement error brought about by the eigenfrequencies.